Mobile communication system and method for registering location of a mobile terminal in the mobile communication system

ABSTRACT

A mobile terminal registration system is provided for a mobile communication system having a plurality of base stations making respective radio zones and a mobile terminal that moves in the radio zone and registers its location to the base stations. The mobile terminal comprises a location registration section for detecting reception levels of signals from the base stations, calculating a difference of the largest reception level and the second reception level and registering the mobile terminal location to a base station that transmits the largest reception level signal if the difference is larger than a threshold value.

BACKGROUND OF THE INVENTION

This invention relates to a system and method for registering locationof a mobile terminal in a mobile communication system, moreparticularly, to a system and method for making an exchange officerecognize a radio zone where the mobile terminal exists to controlcommunication.

Conventionally, methods for making an exchange office control locationof a mobile terminal that moves in a plurality of radio zones made up bya plurality of base stations are proposed, for example, one of them isdisclosed in Japanese Patent Laid Open No. 71226 (1989).

In this method, a location display unit provided in an exchange officereceives location information of a mobile terminal as well as a mobileterminal number and displays the location information of a mobileterminal. Then, location of the mobile terminal is recognized andcontrolled.

In this conventional location control method, as shown in FIG. 6 forexample, a plurality of base stations B1 to B3 are connected with anexchange office A. The base stations make radio zones Z1 to Z3,respectively. A mobile terminal C receives one or more control signalsfrom the base stations. If there are multiple control signals, themobile terminal C registers its location to a base station havingtransmitted a control signal of which reception level is largest.According to this location registration, the exchange office A acquireslocation information of the mobile terminal via a base station havingbeen registered the location. The location information acquired isdisplayed on the location display unit provided in the exchange officeA.

In such a conventional method, when the mobile terminal moves to an areaof a base station to which the mobile terminal registers its locationoverlapped with a neighboring radio zone from an area not overlappedwith the neighboring radio zone, if a reception level of signal from thebase station having been registered the location is more than a presetlevel, the mobile terminal does not register its location to the basestation of the neighboring radio zone even if the reception level ofsignal from the neighboring base station is larger than the receptionlevel of signal from the base station to which the mobile terminalregisters its location. Therefore, the exchange office A can notrecognize that the mobile terminal C has moved to the radio zone ofneighboring base station.

To solve this problem, the mobile terminal compares reception levelsfrom a plurality of base stations and register its location to a basestation that transmits a signal of largest reception level in the areawhere radio zones overlap. In this method, the mobile terminal canregister its location to the nearest base station, so the exchangeoffice can properly control location of the mobile terminal.

However, in this method, if the mobile terminal is in an area wherereception levels from neighboring base stations are nearly equal, themoving mobile terminal may frequently change the base station to beregistered location. As a result, it may occur confusion on locationcontrol of the mobile terminal.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the aforementionedproblems.

It is another object of the present invention to provide a mobilecommunication system enabling to properly and immediately controllocation registration of a mobile terminal in an exchange office.

It is still another object of the present invention to provide a methodfor registering location of a mobile terminal wherein an exchange officecan immediately confirm location of a mobile terminal and properlyconduct location control of the mobile terminal.

The object of the present invention is achieved by a mobilecommunication system having a plurality of base stations, each of thebase stations makes a radio zone, and a mobile terminal that moves inthe radio zones and registers location of the mobile terminal to apredetermined base station, wherein the mobile terminal compriseslocation registration means for detecting reception levels of signalsfrom the base stations, calculating a difference between a largestreception level and a second largest reception level and registeringlocation of the mobile terminal to a base station having transmitted asignal of the largest reception level when the difference is larger thana preset threshold value.

The object of the present invention is further achieved by a method forregistering location of a mobile terminal in a mobile communicationsystem having a plurality of base stations, each of the base stationsmakes a radio zone, and a mobile terminal that moves in a plurality ofradio zones, in the mobile terminal, comprising steps of:

detecting a plurality of reception levels of a plurality of signals fromthe base stations;

selecting a largest reception level and a second largest reception levelfrom among detected reception levels;

calculating a difference between the largest reception level and thesecond largest reception level; and

registering location of the mobile terminal to a base station havingtransmitted a signal of the largest reception level when the differenceis lager than a preset threshold value.

In the present invention, changes of location registration are notconducted in an area where reception levels of signals from neighboringbase stations are nearly equal and a change of location registration isconducted when a difference of reception levels of signals becomes lagerthan a preset threshold value as the mobile terminal moves. So thefrequency of changing location registration becomes low and confusion oflocation control in the exchange office becomes avoidable.

Furthermore, the exchange office comprises a location display unit fordisplaying location of the mobile terminal. The location display unithas a map indicating divisions of the base stations and displayslocation of the mobile terminal in a division of the base stationaccording to a signal from a base station having been registeredlocation of the mobile terminal. As a result, location of the mobileterminal can be confirmed immediately.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects, features and advantages of the present inventionwill become more apparent upon a reading of the following detaileddescription and drawings, in which:

FIG. 1 illustrates a system configuration of a first embodiment;

FIG. 2 is a figure for explaining a signal format;

FIG. 3 is a block diagram of a mobile terminal;

FIG. 4 is a figure showing a typical status of reception levels ofsignals;

FIG. 5 illustrates a system configuration of a second embodiment; and

FIG. 6 is a figure for explaining a prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention is described.

In the first embodiment, two radio zones partially overlap each other.

FIG. 1 illustrates a system configuration to explain the firstembodiment of the present invention.

In this system, a plurality of base stations B1 to B3 make radio zonesZ1 to Z3, respectively, radio zones of neighboring base stationspartially overlap each other.

The base stations B1 to B3 are connected to an exchange office A,respectively. The base stations B1 to B3 can transmit/receive a signalto/from the exchange office A.

The exchange office A has a location display unit D. The locationdisplay unit D has a map where location of the base stations B1 to B3 isregistered and a mobile terminal C is displayed on the map according tothe base station having been registered location of the mobile terminal.When the mobile terminal C currently registers its location to the basestation B3, for example, the mobile terminal C is displayed in thedivision of the base station B3 on the location display unit D. Then,the exchange office A can confirm existence of the mobile terminal C asit is in the vicinity of the location of the base station B3. Accordingto this data, the exchange office A can conduct location control of themobile terminal C.

Next, a signal used for the embodiment is described.

A signal format used for the embodiment is the same as that of PersonalHandy-phone System (referred to as PHS, hereinafter).

In PHS, a TDMA frame is used for a transmission/reception signal. A TDMAframe has four slots for transmission and reception, respectively. Thesignal format of each slot has a transmission identification code and areception identification code as shown in FIG. 2. In the presentembodiment, the mobile terminal C identifies the transmitter of areception signal using the transmission identification code. The abovesignal format is describes in detail in "PERSONAL HANDY PHONE SYSTEM RCRSTANDARD VERSION 1, RCR STD-28" issued by Research & Development Centerfor Radio System (RCR) on Dec. 20, 1993.

Next, the configuration of the mobile terminal C is described.

FIG. 3 is a block diagram of the mobile terminal C.

In FIG. 3, the numeral 1 is a radio section for receiving signals fromthe base stations B1 to B3.

The numeral 2 is a level detection section for detecting a receptionlevel of a received signal. It identifies each transmitter of areception signal based on a transmission identification code included inthe reception signal if two reception signals have been input. Also, itgenerates identification information indicating a transmitter of thesignal based on the transmission identification code included in areception signal of which reception level is larger than the others andoutputs it to a base station setting section 7 described later.

The numeral 3 is a calculation section. It calculates an absolute valueof a difference of reception levels of two signals output from the leveldetection section 2.

The numeral 4 is a threshold value setting section, wherein a thresholdvalue is preset in advance.

The numeral 5 is comparison section. It compares a reception leveldifference output from the calculation section 3 and the presetthreshold value in the threshold value setting section 4 and outputs alocation registration requirement signal when the reception leveldifference is larger than the threshold value.

The numeral 6 is a memory for storing an identifier of a base station towhich the mobile terminal C currently registers its location.

The numeral 7 is a base station setting section. When the locationregistration requirement signal is input, the base station settingsection 7 compares a base station indicated by an identifier stored inthe memory 6 and a base station indicated by identification informationoutput from the level detection section 2. When the base stationindicated by the identifier and the base station indicated by theidentification information are different each other, the base stationsetting section 7 registers location to the base station indicated bythe identification information and updates the content of the memory 6by an identifier of the base station to which it newly has registeredlocation. While, when a base station indicated by an identifier and abase station indicated by identification information is the same eachother, location registration is not conducted.

Next, operations of the first embodiment are described.

Here, a threshold value set in the threshold value level setting section4 is 5 dB in the following explanations.

[Case-1]

The mobile terminal C is in the zone Z3 of the base station B3. (In thiscase, the mobile terminal C is shown by a solid line in FIG. 1).

Here, the case that the mobile terminal C is in the zone Z3 of the basestation B3, the mobile terminal C can receive a signal from the basestation B3 but can not receive a signal from the base station B2 isexplained. Where, the mobile terminal C had registered its location tothe base station B3.

First, the mobile terminal C receives the signal from the base stationB3 with the radio section 1.

The level detection section 2 detects a reception level of signal fromthe base station B3 and outputs a result to the calculation section 3.The reception level at this time is assumed as 7 dB.

In Case-1, the mobile terminal C can not receive other than the signalfrom the base station B3, so there is no signal to be detected. Then,the level detection section 2 generates identification informationindicating the base station B3 according to a transmissionidentification code included in the reception signal, and outputs theidentification information to the base station setting section 7.

The calculation section 3 calculates a reception level difference. Inthis case, the detected reception level is only 7 dB, so the receptionlevel difference is also 7 dB.

The comparison section 5 compares the reception level difference 7 dBand the threshold value 5 dB. In this case, the reception leveldifference is larger than the threshold value. Therefore, the comparisonsection 5 outputs a location registration requirement signal.

When receiving the location registration requirement signal, the basestation setting section 7 compares a base station indicated anidentifier stored in the memory 6 and a base station indicated byidentification information. Here, the base station indicated by theidentifier stored in the memory 6 is the base station B3, the basestation indicated by the identification information is also the basestation B3. Therefore, two base stations are the same, so the basestation setting section 7 does not register the location to the basestation B3 again.

[Case-2]

The mobile terminal C is in an area where the zone Z3 of the basestation B3 and the zone Z2 of the base station B2 partially overlap. (Inthis case, the mobile terminal C' is shown by a broken line in FIG. 1)

Here, the case that the mobile terminal C moves to the radio zone Z2 ofthe neighboring base station B2 from the radio zone Z3 of the basestation B3 and it reaches to the area where both radio zones overlap isexplained.

At this time, the mobile terminal C receives a signal from the basestation B3 having been registered location by the mobile terminal C anda signal from the base station B2. FIG. 4 typically shows a status ofreception level.

The level detection section 2 respectively detects reception levels ofsignals from the base stations B2 and B3. If assuming that the receptionlevel of the signal from the base station B2 is 2 dB and that from thebase station B3 is 5 dB, the level detection section 2 generatesidentification information B3 indicating the base station B3.

Next, the calculation section 3 calculates a difference between bothreception levels. In this case, the reception level difference is 3 dB.

The comparison section 5 compares the reception level difference 3 dBand the threshold value 5 dB. Here, the threshold value is larger thanthe reception level difference. Therefore, location registrationrequirement signal is not output.

The base station setting section 7 does not receive the locationregistration requirement signal, it does not register the location.

As the mobile terminal C moves nearer to the base station B2, thereception level of the signal from the neighboring base station B2becomes larger, so the difference of reception levels of signals fromboth base stations gradually becomes small, finally it becomes zero whenboth reception levels of signals become the same. Therefore, the value,level difference, output from the calculation section 3 becomes smallerthan the threshold value level. In this case, described as above, thecomparison section 5 does not output the location registrationrequirement signal to the base station setting section 7, so theregistered location is kept as it is.

When the mobile terminal C moves to the side nearer to the base stationB2 than the base station B3, the reception level of signal from the basestation B2 is larger than that from the base station B3.

Here, it is assumed that the level detection section 2 detects 2 dBreception level of signal from the base station B3 and 8 dB receptionlevel of signal from the base station B2. Then, the level detectionsection 2 generates identification information indicating B2, becausethe reception level of signal from the base station B2 is larger.

The calculation section 3 calculates a difference of reception levels ofboth signals. In this case, the reception level difference is 6 dB.

The comparison section 5 compares the reception level difference 6 dBand the threshold value 5 dB. In this case the reception leveldifference is larger than the threshold value. Therefore, a locationregistration setting requirement signal is output.

When receiving the location registration setting requirement signal, thebase station setting section 7 compares a base station indicated by anidentifier stored in the memory 6 and a base station indicated byidentification information. In this case, the base station stored in thememory 6 is the base station B3 and the base station indicated by theidentification information is the base station B2. Therefore, two basestations are not the same, so the base station setting section 7registers the location to the base station B2.

As a result of this location registration, the mobile terminal isdisplayed in the division of the base station B2 on the map of thelocation display unit D in the exchange office, so the exchange officecan confirm that the mobile terminal C is near the base station B2.

Like this, when the mobile terminal C moves from a radio zone from whichthe mobile terminal C is receiving a signal of reception level largerthan a preset reception level to another neighboring radio zone via anarea where both radio zones overlap, a base station to be registeredlocation of the mobile terminal C can be automatically changed if asignal from the neighboring base station is larger than the presetreception level and the reception level difference is larger than thethreshold value level.

Through these operations, the exchange office can immediately confirmthe location of the mobile terminal C and properly conduct locationcontrol.

In addition, also in an area where the reception level difference isnearly zero, change of location registration is not done. When thereception level difference has exceeded the threshold value levellocation registration is changed. So, the number of changes of locationregistration can be reduced, resulting to avoid confusion in locationcontrol of the mobile terminal.

Next, a second embodiment is explained.

The second embodiment is a case that three radio zones partiallyoverlap.

FIG. 5 illustrates a system configuration to explain the secondembodiment of the present invention.

In this system, the base station B4 making a radio zone Z4 is added tothe first embodiment shown by FIG. 1, and the three radio zones Z2, Z3and Z4 partially overlap.

The base station B4 is connected with the exchange office A, cantransmit/receive a signal to/from the exchange office A. Also, adivision of the base station B4 is added on the location display unit Din the exchange office A.

In this second embodiment, a mobile terminal receives three signals fromthree base stations in an area where three radio zones Z2, Z3 and Z4partially overlap. Therefore, the level detection section 2 selects andoutputs a largest reception level and a second largest reception levelto the calculation section 3 after detected three reception levels. Inaddition, it generates identification information indicating a basestation that transmits the largest reception level signal. The othercomponents are the same as those of the first embodiment, soexplanations for them are omitted.

Next, operations of the second embodiment are explained. The thresholdvalue that is set in the threshold value setting section 4 is assumed as5 dB.

[Case-1]

The mobile terminal C is in the zone Z3 of the base station B3. (In thiscase, the mobile terminal C is shown by a solid line in FIG. 5).

Here, the case that the mobile terminal C is in the zone Z3 of the basestation B3, the mobile terminal C can receive a signal from the basestation B3 but can not receive any signals from other base stations isexplained.

In this case, only the signal from the base station B3 is received, sothe largest reception level is a reception level from the base stationB3. The other reception levels are 0 dB.

Accordingly, the level detection section 2 detects a reception level ofsignal from the base station B3, generates and outputs identificationinformation indicating the base station B3.

After these operations, the system operates similarly to the Case-1 ofthe first embodiment.

[Case-2]

The mobile terminal C is in an area where the radio zones Z2, Z3 and Z4partially overlap each other. (In this case, the mobile terminal C' isshown by a broken line in FIG. 5)

It is assumed that the mobile terminal C moves from the radio zone Z3,which does not overlap with any radio zones, of the base station B3 towhich the mobile terminal C registers its location to an area where theradio zones Z2, Z3 and Z4 partially overlap each other.

In this case, the mobile terminal C receives a signal from the basestation B3 to which the mobile terminal C registers its location andsignals from neighboring base stations B2 and B4.

The level detection section 2 detects reception levels of signals fromrespective base stations.

Here, it is assumed that the reception levels of signals from the basestations B2, B3 and B4 are 2 dB, 5 dB and 1 dB, respectively.

Then, the level detection section 2 selects the largest reception level5 dB and the second largest level 2 dB. The signal of the largestreception level 5 dB is a signal from the base station B3, soidentification information indicating the base station B3 is generated.

Continuously, the calculation section 3 calculates a difference of bothreception levels. The reception level difference is 3 dB.

The comparison section 5 compares the reception level difference 3 dBand the threshold value 5 dB. In this case, the threshold value islarger than the reception level difference. Therefore, a locationregistration requirement signal is not output.

The base station setting section 7 does not receive any locationregistration requirement signal, so it does not conduct locationregistration.

When the mobile terminal comes close to B2, the reception level ofsignal from the base station B2 becomes larger and the differencebetween reception levels of base stations B2 and B3 becomes zero.Accordingly, the level difference output from the calculation section 3becomes smaller than the threshold value level. At this time, describedas above, the comparison section 5 does not output a locationregistration requirement signal to the base station setting section 7,so base station setting is not changed. The location registration iskept as it is.

When the mobile terminal C moves nearer to the base station B2 than thebase station B3, the reception level of signal from the base station B2becomes larger than that from the base station B3.

Here, it is assumed that the level detection section 2 detects receptionlevels of signals 2 dB, 8 dB and 1 dB from the base stations B3, B2 andB4, respectively.

Then, the level detection section 2 selects the largest reception level8 dB and the second largest reception level 2 dB, and generatesidentification information indicating the base station B2.

The calculation section 3 calculates a difference of both receptionlevels. The reception level difference is 6 dB.

The comparison section 5 compares the reception level difference 6 dBand the threshold value 5 dB. In this case, the reception leveldifference is larger than the threshold value. Therefore, a locationregistration requirement signal is output.

When receiving the location registration requirement signal, the basestation setting section 7 compares a base station indicated by anidentifier stored in the memory 6 and a base station indicated byidentification information. Here, the base station indicated by theidentifier stored in the memory 6 is the base station B3, the basestation indicated by the identification information is the base stationB2. The compared base stations are not the same, so the base stationsetting section 7 registers location of the mobile terminal to the basestation B2.

As a result of this location registration, the mobile terminal C isdisplayed in the division of the base station B2 on the map of thelocation display unit D in the exchange office A, so the exchange officecan confirm that the mobile terminal C is near the base station B2.

Like this, even if there are three or more neighboring base stations andoverlapped radio zones and reception levels of signals from them are thesame level, change of location registration is not done throughoperations including calculation of a reception level difference of thelargest reception level and the second largest reception level. When thereception level difference has exceeded a preset threshold value level,location registration is changed.

Accordingly, the number of changes of location registration can bereduced, resulting to avoid confusion in location control of the mobileterminal.

What is claimed is:
 1. A mobile communication system comprising aplurality of base stations, each of said base stations forming a radiozone, and a mobile terminal that moves in said radio zones, wherein saidmobile terminal comprises location registration means for registering alocation of said mobile terminal to one of said base stations, saidlocation registration means comprising:means for receiving a pluralityof signals from said base stations; means for detecting reception levelsof said signals, selecting a largest reception level and a secondlargest reception level from among said reception levels and generatingidentification information indicating a base station having transmitteda signal of said largest reception level based on said signal ofselected largest reception level; means for calculating a differencebetween said largest reception level and said second largest receptionlevel; means for comparing said difference and a present thresholdvalue; and location registration establishment means for registering thelocation of said mobile terminal to a base station indicated by saididentification information when said difference is larger than saidthreshold value, where said location registration establishment meansdoes not register location of said mobile terminal to said base stationindicated by said identification information when said difference issmaller than said threshold value.
 2. The mobile communication system ofclaim 1, wherein said location registration means furthercomprises:storage means for storing an identifier of a base stationhaving been registered location; and means for comparing a base stationindicated by said identification information and a base stationindicated by said identifier when said difference is larger than saidthreshold value, and for registering the location of a mobile terminalwhen said base station indicated by said identification information andsaid base station indicated by said identifier stored in said storagemeans are different.
 3. The mobile communication system of claim 1,further comprising an exchange office connected with said base stationsand for receiving location information of said mobile terminal via abase station to which the location of said mobile terminal has beenregistered and confirming the location of said mobile terminal, whereinsaid exchange office comprises location display means having a mapindicating divisions of said base stations and for displaying thelocation of said mobile terminal in a division of said base stationbased on a signal from a base station having been registered location ofsaid mobile terminal.
 4. A mobile communication system comprising anexchange office, a plurality of base stations, each of said basestations makes a radio zone, and a mobile terminal that moves in a saidradio zones, where said mobile terminal registers a location of saidmobile terminal to a predetermined base station and said exchange officereceives location information of said mobile terminal via saidpredetermined base station and said exchange office the confirmslocation of said mobile terminal, wherein said mobile terminalcomprises:means for receiving a plurality of signals from a plurality ofbase stations; means for detecting reception levels of said signals,selecting a largest reception level and a second largest reception levelfrom among said reception levels and generating identificationinformation indicating a base station having transmitted a signal ofsaid largest reception level according to selected largest receptionlevel; means for calculating an absolute value of a difference betweensaid largest reception level and said second largest reception level;means for comparing said absolute value of said difference and a presetthreshold value; storage means for storing an identifier of a basestation to which the location of said mobile terminal has beenregistered; means for comparing a base station indicated by saididentification information and a base station indicated by saididentifier when said absolute value of said difference is larger thansaid threshold value where said means does not register location of saidmobile terminal when said base station indicated by said identificationinformation and said base station indicated by said identifier stored insaid storage means are the same, and for registering the location of amobile terminal when said base station indicated by said identificationinformation and said base station indicated by said identifier stored insaid storage means are different, where said means does not register thelocation of said mobile terminal when said absolute value of saiddifference is smaller than said threshold value; and said exchangeoffice comprises: location display means having a map indicatingdivisions of said base stations for displaying and for displaying thelocation of said mobile terminal in a division of said base stationaccording to a signal from a base station to which the location of saidmobile terminal has been registered.
 5. A mobile communication systemcomprising a plurality of base stations, each of said base stationsforming a radio zone, and a mobile terminal that moves in said radiozones, wherein said mobile terminal comprises location registrationmeans for registering a location of said mobile terminal to a basestation, said location registration means comprising:means for receivingtwo signals from two base stations; means for detecting reception levelsof said signals; means for calculating a difference between tworeception levels of the two signals from among said signals; means forcomparing said difference and a preset threshold value; storage meansfor storing an identifier of a base station to which the location of amobile terminal has been registered; means for comparing a base stationhaving transmitted a signal of a larger reception level and a basestation indicated by said identifier when said difference is larger thansaid threshold value where said means does not register the location ofsaid mobile terminal when said base station having transmitted a signalof a larger reception level and said base station indicated by saididentifier are the same, and for registering the location of a mobileterminal to a base station having transmitted a signal of a largerreception level when said base station having transmitted a signal of alarger reception level and said base station indicated by saididentifier stored in said storage means are different, where said meansdoes not register the location of said mobile terminal when saiddifference is smaller than said threshold value.
 6. The mobilecommunication system of claim 5, further comprising an exchange officeconnected with said plurality of base stations and receiving locationinformation of said mobile terminal via a base station having beenregistered location of said mobile terminal and confirming location ofsaid mobile terminal, wherein said exchange office compress locationdisplay means having a map indicating divisions of said base stationsand for displaying the location of said mobile terminal in a division ofsaid base station according to a signal from a base station to which thelocation of said mobile terminal has been registered.
 7. A method forregistering location of a mobile terminal in a mobile communicationsystem having a plurality of base stations, each of said base stationsmakes a radio zone, and a mobile terminal that moves in a plurality ofradio zones, in said mobile terminal, the method comprising stepsof:detecting a plurality of reception levels of a plurality of signalsfrom said base stations; selecting a largest reception level and asecond largest reception level from among detected reception levels;calculating a difference between said largest reception level and saidsecond largest reception level; and registering the location of saidmobile terminal to a base station having transmitted a signal havingsaid largest reception level when said difference is larger than apreset threshold value; and displaying location of said mobile terminalin a division of said base station on a map indicating divisions of saidbase stations in said exchange office based on a signal from a basestation to which the location of said mobile terminal has beenregistered.
 8. The method for registering location of a mobile terminalin a mobile communication system of claim 7, wherein said method doesnot register the location of said mobile terminal when said differenceis smaller than said threshold value in said location registration step.9. The method for registering location of a mobile terminal in a mobilecommunication system of claim 7, wherein said location registration stepfurther comprises steps of:confirming whether said base station havingtransmitted a signal of largest reception level is registered locationof said mobile terminal; and registering the location of said mobileterminal to said base station when location of said mobile terminal hasnot been registered, where location registration to said base station isnot conducted when location registration has been done already.
 10. Themethod for registering location of a mobile terminal in a mobilecommunication system of claim 7, wherein said difference of receptionlevels is an absolute value of a difference between a largest receptionlevel and a second largest reception level.
 11. The method forregistering location of a mobile terminal in a mobile communicationsystem of claim 7, wherein said step of location registration is a stepof locating registration to said base station by using identificationinformation, that is included in said signals, indicating a base stationhaving transmitted said signal.